Embodiments of the subject matter described herein relate to systems and methods for determining operating parameters for traction motors in a vehicle system.
At least some known vehicle systems have propulsion systems that include multiple traction motors. The traction motors are operated as a group to collectively propel the vehicle system along a route. For instance, various propulsion systems have been developed for locomotives. In one type of propulsion system, the traction motors are individually controlled to propel the locomotive along the designated route. Each of the traction motors may be energized by a separate inverter that is individually controlled to adjust an excitation frequency of the respective traction motor. The excitation frequency controls the rotation of the traction motor, which drives a corresponding axle that is coupled to a wheel of the locomotive. Although each of the traction motors can be controlled individually, the propulsion system coordinates operation of the traction motors to achieve a total tractive effort for the locomotive. This type of propulsion system may be referred to as a “per-axle” system, because each axle is driven by an individually-controlled traction motor.
In another type of propulsion system, a set of traction motors are supported by a common truck. The traction motors of the truck may be in parallel or in series and energized by a common inverter. As such, each of the traction motors receives the same excitation frequency from the inverter. Assuming that each of the traction motors is of the same motor type (e.g., designed to provide the same motor performance) and the wheel diameters are equal, the traction motors supply an equal amount of tractive effort because the traction motors receive the same excitation frequency. Locomotives having this type of propulsion system typically include two trucks. This type of propulsion system is referred to as a “per-truck” system, because the multiple traction motors of the truck are controlled by a single inverter.
In many cases, the traction motors for one type of propulsion system are designed to provide a designated motor performance, which may differ from the motor performances of other propulsion systems. By way of example, in per-truck systems, it is generally desirable to have traction motors with high resistance rotors. The overall performance of a per-truck system can be sensitive to differences in wheel diameters. Although the traction motors receive the same excitation frequency, the traction motors will provide different amounts of torque if the wheel diameters of the wheels that are coupled to the traction motors are unequal. This may lead to undesirable motor heating, motor losses, and/or reduced performance. Traction motors having high resistance rotors are used in per-truck systems because such traction motors reduce the sensitivity of the propulsion system to unequal wheel diameters. Although per-axle systems may also have wheels with different diameters, the per-axle systems are capable of individually controlling the axles to reduce the negative effects of the unequal wheel diameters. With the sensitivity to unequal wheel diameters being less of a concern, traction motors in per-axle systems are permitted to use low resistance rotors, which can be more efficient than high resistance rotors.
In the past, railroads typically used locomotives having the same type of propulsion system and, consequently, the same type of traction motor. Recently, however, railroads have begun to use different types of propulsion systems. During the lifetime operation of a locomotive, the traction motors of the propulsion system may be replaced. It may be possible that the traction motor configured for one type of propulsion system will be installed into a propulsion system of another type. If this occurs, it may not be readily apparent to the operator or the control system of the locomotive that the traction motor is unsuitable. Nevertheless, continued operation of the locomotive with the improper traction motor may compromise the overall performance of the propulsion system, increase a likelihood of motor failure, or cause other unwanted effects to the traction motor or the propulsion system.